It is a known practice to control the automatic operation of movable home automation equipment items comprising a movable element, for example a roller blind, a garage door, a linear movement gate, a rotary movement gate, a Venetian blind with horizontal slats, a pivoting window. This control uses information originating from one or more sensors, as described, for example, in patent application US 2001/000294.
This or these sensors are placed either inside the actuator of the home automation equipment item, or directly at the movable element.
When the sensor is in the actuator, it measures for example the rotation of the motor output shaft, or else the rotation of the output shaft of the reduction gear driven by the motor, or else if a jack is involved, the linear movement of the rod of the latter. In certain cases, the sensor measures an electric quantity that is the image of the speed of the motor: for example the voltage at the terminals of the phase displacement capacitor, if it involves a single-phase induction motor and running capacitor, or for example the electromotive movement force if it involves a direct current motor with permanent magnets.
The problem posed by these devices is that there is usually no proportional relation between the measured quantity and the movement of the movable equipment.
In the case of a roller blind for example, the panel of the blind rolls up on a tube. The result of the thickness of the panel is that the rolling radius increases as the blind opens. Depending on the nature of the panel, one and the same rotational movement value seen by the motor may give rise to very different panel movement values depending on whether the panel arrives at a top stop (maximum rolling diameter) or at a bottom stop (minimum rolling diameter). The result of this is a real difficulty in controlling the force that is not to be exceeded when the panel arrives in contact with a stop or an obstacle.
In the case of a tilting garage door, the vertical movement of the bottom of the door also obeys a nonlinear relation with the rotation of the drive motor making it possible to move a carriage on a horizontal rail. This is again reflected in very significant differences in the relation linking the motor torque and the force applied to the door, depending on the degree to which the latter is open. To control the force not to be exceeded when the door arrives in contact with an obstacle, it is a known practice to carry out a learning operation, making it possible, for example, to cut the trajectory into zones and adjust the value of the motor torque so that it is slightly greater than the necessary torque.
In the case of a Venetian blind with horizontal slats comprising a single motor, a device called a “tipper”, driven by the rotation shaft, acts on ladders supporting the slats of the panel. The rotation of the rotation shaft causes that of the tipper and hence a greater or lesser inclination of the slats. In certain sunlight conditions, a minimal difference between the inclinations of the tippers of two adjacent Venetian blinds is enough to cause a very different visual effect. For the correct architectural uniformity of a facade, and the visual comfort of the occupants, it is important that the various equipment items are in the same state and hence to identify and reproduce precisely the angular positions of the motor corresponding to the extreme positions of the tipper. However, the actuators used to drive Venetian blinds most frequently comprise a rotation sensor placed at the output of the motor and not at the output of the reduction gear. The result of this is that the clearance of the reduction gear and, as a consequence, the compensation for the clearance that takes place during each inversion of direction, considerably influence the relation that exists between the value supplied by the sensor and the position of the home automation equipment item, so this relation has a hysteretic appearance. In addition, the intensity of the clearance is not constant but depends on the load applied, hence on the greater or lesser deployment of the Venetian blind panel. If the rotational control of the motor is applied directly based on the time of operation and not with a rotation sensor, the situation is yet worse because the times of opening and of locking the immobilization brake and/or the times for actuating the activation relays of the motor also play a part.
To remedy these various disadvantages, associated with the nonlinearity of the relation between input and output quantities, it is a known practice in certain cases to place the movement sensor directly on the movable element. Such a sensor then usually requires a physical contact between a fixed portion and a movable portion of the equipment.